Copper (1) salt-hydrophilic binder lithographic images

ABSTRACT

A lithographic printing plate having an ink-receptive image comprising a hydrophilic colloid binder, an insoluble salt or complex of copper (I) with an oleophilogenic compound, and metallic silver is made by treating a hydrophilic colloid-silver image with an activator containing cupric ions and said oleophilogenic compound. Activators are aqueous solutions containing copper (II) ions and a halogen ion.

ite States ate Blake 1 June 5, 1973 [54] COPPER (l) SALT-HYDROPHILIC BINDER LITHOGRAPHIC IMAGES [75] Inventor: Ralph Kingsley Blake, Westfield,

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Aug. 3, 1970 [21] Appl. No.: 60,619

Related US. Application Data [63] Continuation-impart of Ser. No. 864,867, Oct. 8,

1969, abandoned.

[52] US. Cl. ..101/456, 96/33, 96/29 L, 101/466 [51] Int. Cl ..B4ln l/00, B41n 3/00, G031" 7/02 [58] Field of Search ..96/33, 29 L, 29 R; 101/456, 459, 466

[56] References Cited UNITED STATES PATENTS 3,511,656 5/1970 Regan et a] ..96/33 X 3,083,097 3/1963 Lassig et al. ..96/33 X 3,490,905 l/l970 Blake .'....96/33 X 3,257,941 6/l966 Wolfson et al. ..96/29 L X Primary Examiner-David Klein Attorney-James T. Carle [57] ABSTRACT 11 Claims, No Drawings COPPER (1) SALT-HYDROPHILIC BINDER LITIIOGRAPHIC IMAGES CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 864,867, filed Oct. 8, 1969 and now abandoned.

An element useful in making images of the type disclosed in this application is described in Assignees copending application by Blake, filed Aug. 4, 1969, Ser. No. 847,399, which now US. Pat. No. 3,635,399, also discloses and claims activator solutions BACKGROUND OF THE INVENTION This invention relates to lithographic printing plates and more particularly to improved colloid lithographic plates. Still more particularly it relates to lithographic images on colloid plates having improved quality and press life.

Methods of preparing lithographic images from gelatino-silver images are well known.

An exposed gelatino-silver halide emulsion layer may be treated with a tanning developer which hardens the gelatin in the imaged areas and makes it ink-receptive. In the bromoil process oleophilic hardened gelatin images are produced by treating a gelatino-silver image (produced by conventional photographic methods) with a tanning bleach which hardens the gelatin in the silver image areas of the ayer but does not affect those portions of the gelatin layer having no silver. The silver in a gelatino-silver image may also be used to catalyze the oxidative degradation of the gelatin in the imaged areas so that it can be washed away to reveal an oleophilic underlayer.

Lassig, et al., US. Pat. No. 3,083,097 disclose a process for making a lithographic image from a gelatinosilver image by converting the silver image into an image of heavy metal and/or silver compounds and reacting these with sparingly soluble organic compounds containing Sl-I, SeH, OH, or NH groups to form organic salt-like or complex compounds which are less soluble than the original products of oxidation. The presence of the organic salt-like or complex com pounds makes the imaged areas oleophilic and therefore ink-receptive. In the Lassig, et al., process all of the superficial silver image is converted to a silver salt in the first step, then in a second step this silver salt is further reacted with a sparingly soluble organic compound to form the oleophilic image. Prior art processes are long and difficult and produce plates capable of printing relatively few copies before they are worn out. The lithographic images of this invention are easily prepared and are very durable so that they may be used to print many thousands of copies.

SUMMARY OF THE INVENTION It is an object of this invention to prepare from colloido-silver halide emulsion layers more durable lithographic plates having improved image quality and longer press life. A further object is to prepare such plates by improved and simpler processes.

The improved lithographic images of this invention comprise a hydrophilic colloid binder capable of forming a complex with copper (I) ion, an insoluble complex or salt of copper (I) ion with an oleophilogenic compound and metallic silver.

The process for making lithographic images comprises exposing imagewise a photographic element comprising a support bearing a layer of a dispersion of light-sensitive silver halide in a macromolecular organic protein colloid binder; developing the exposed layer with a silver halide developing agent to form a silver image; treating the developed silver image with an aqueous solution containing a. a water-soluble, inorganic copper salt yielding copper (II) ions in a concentration of 0.01 molar to about 2.0 molar,

b. a water-soluble, inorganic halide yielding a halogen ion forming a silver salt no more soluble in water than silver chloride in a concentration of 0.01 to 0.5 molar,

to reduce copper (II) ions, the reduction being terminated before all superficial silver image is oxidized, characterized in that an oleophilogenic compound is present l) at least when the element is treated with the aqueous solution or (2) after formation of copper (1) ions.

These lithographic images are simply and conveniently formed by treating a colloido-silver image with a solution comprising copper (II) ions and the sulfuror nitrogen-containing organic compound until the metallic silver has reduced enough copper (II) ions to copper (I) ions, which form an insoluble complex with said oleophilogenic organic compound to make an inkreceptive image. This treatment should be discontinued before all of the superficial silver image has reacted with copper (II) so that the remaining silver can provide the metallic silver component of the lithographic image. This oleophilogenic compound can also be added after formation of copper (I) ions.

To obtain the lithographic images, activator solutions are used in the process. The activator solution comprises an aqueous solution having a pH of 0.5 to 6.0, preferably between 1 and 3, and contain a. copper (II) ions in a concentration of 0.01 molar to about 2.0 molar;

b. a water-soluble, inorganic halide yielding a halogen ion forming a silver salt no more soluble in water than silver chloride in a concentration of 0.01 to 0.5 molar;

and are characterized in that the activator contains at least one of the following 1. an oleophilogenic compound in a concentration of 0.1 to 10 grams or more per liter of the solution;

2. a mild oxidizing agent in a concentration such that the ratio of copper (II) to oxidizing agent is between 1 to 5 and to 1.

Useful oleophilogenic compounds are described below. Suitable mild oxidizing agents which can be present in the activator, either in combination with the oleophilogenic compound or not, include, e.g., iron (III) ion, benzoquinone, mercury (II) chloride, in a concentration ratio to copper (II) ion of from about 5/1 to H100, preferably from 3/1 to l/30. Such oxidizing agents have been found to reduce or prevent background scum on the plates.

Citric acid and other complexing agents may be used to control available copper (II) ion concentration. Other adjuvants such as 1,2,3-triphenyl guanidine and cyanoguanidine may be added to the activator solution to give the plate a more rapid start-up capability.

The resulting lithographic plates start to print rapidly on the press, have a long press life (up to 30,000 copies or more).

DESCRIPTION OF THE PREFERRED EMBODIMENTS The hydrophilic binder for the lithographic images is a stratum of a film-forming colloid-containing chemical groups capable of forming complexes or salts with copper (I) ions, thus binding them to said stratum. A preferred such binder is gelatin, although any hydrophilic binder capable of forming a strong complex or salt with copper (I) ions may be used, e.g., other macromolecular proteins, including casein and zein.

The binder preferably should form stronger complexes with copper (I) ions than with copper (II) ions. The binder should be hardened sufficiently so that none of the colloid is transferred to the printed surface.

The copper (I) ions which are distributed imagewise in the ink-receptive portions of the lithographic image may be produced by any appropriate means for generating an image of copper (I) ions. A copper (I) solution may be applied mechanically as with a pen or a gravure printing press. A particularly preferred method of producing a copper (I) ion image is to generate copper (I) ions by imagewise reduction of copper (II) ions using a metallic silver image as the reducing agent. This may be done by treating the colloido-silver image with an aqueous solution of copper (II) ions in a concentration of 0.01 to 2.0 moles per liter, and a suitable anion, e.g., a halide forming a silver salt no more soluble in water than silver chloride, in a concentration of from about 0.01 to about 0.5 molar, preferably between 0.01 and 0.1 molar.

The metallic silver component of the image is required for a long-lived lithographic image. In the absence of metallic silver the lithographic image deteriorates fairly rapidly. A preferred method of producing the metallic silver in intimate association with the copper (I) ion image is to produce said image by using a metallic silver image to reduce copper (II) ions, stopping the process before all of the superficial silver image is oxidized. This may be achieved by'stopping the reduction while at least some silver image is still visible.

The oleophilogenic compound used in this invention is a compound which forms an insoluble salt or complex with copper (I) ions and an appreciably more soluble complex or salt with copper (II) ions and at the same time imparts an oleophilic character to the hydrophilic colloid binder. Usually the molecules of such compound will have an oleophilic moiety and a coppercomplexing or salt-forming moiety. The coppercomplexing or salt-forming moiety frequently is comprised of one or more nitrogen, sulfur or oxygen atoms. The oleophilic moiety may be a hydrocarbon residue. Generally speaking, the more soluble the compound is in water, the more effective it will be, for larger concentrations of the molecules will be available to react with the copper (I) ions. The organic compounds preferably contain at least two hetero atoms to be effective in making an oleophilic, ink-receptive image. Nitrogencontaining compounds are usually the most effective but compounds containing sulfur and oxygen may also be used. Particularly preferred compounds are substituted organic indoles, diazoles, triazoles, and tetrazoles. Representative operative compounds are potassium thiocyanate, benzotriazole, Z-mercaptothiazoline, -nitrobenzimidazole, 3-amino-l,2,4-triazole, tannic acid, potassium hexacyanoferrate (II), and potassium hexacyanoferrate (III).

In practicing a preferred embodiment of this invention a conventional photographic gelatino-silver halide emulsion is exposed to actinic radiation through a process transparency, then developed in a conventional silver halide latent image developes to produce a metallic silver image. The developed image is than bathed for 5 to 90 seconds in a bath comprising copper (II) chloride or bromide at a concentration of between 0.05 and 0.5 mole per liter, citric acid at a concentration of 0.01 to 0.25 mole per liter, and benzotriazole at a concentration of 0.1 to 10 grams per liter. The treatment should be stopped before all the superficial silver image is oxidized. After this treatment, the lithographic plate is placed on a press, inked with lithographic ink and used to print offset or direct negative lithographic copies of the original.

The following examples will illustrate the practice of this invention but are not intended to limit its scope.

EXAMPLE I An ortho-sensitized gelatino-silver chlorobromide emulsion having a /30 mole per cent bromide/chloride ratio and containing 111 g of gelatin per mole of silver halide was coated at a coating weight of 88 mg/dm of silver halide on a polyethylene terephthalate film base prepared as described in Example IV of Alles, U.S. Pat. No. 2,779,684. The dried emulsion was then overcoated with a gelatin antiabrasion layer at a coating weight of 2.5 mg/dm of gelatin. A sample of this element was exposed for 10 seconds through a negative halftone and line original with a No. 2 RFL phototlood operated at 22 volts at a distance of 2 feet. The exposed sample was developed in a conventional high pH pmethylaminophenol/hydroquinone developer for 30 seconds at 70 F, bathed in 2 percent acetic acid for 15 seconds, then bathed for 30 seconds in a bleach at a pH of 2 to 6 prepared according to the following procedure.

Solutions A and B were prepared:

Solution A 3 molar potassium bromide (aqueous) 100 ml 3 molar copper (II) nitrate (aqueous) l00 ml 1 molar potassium citrate (aqueous) 50 ml Water to make 1000 ml Solution B Benzotriazole solution 10 ml (1 g/20 ml of ethanol) Water 990 ml Solution B was added to Solution A. The plate was then rubbed with a conventional gum-asphaltumemulsion used commercially for treating lithographic plates, inked with black offset litho ink using a swab moistened with 2 percent acetic acid, mounted on an offset office duplicator (A.B.Dick) and used to print several hundred offset copies on bond paper using 2 percent acetic acid as the fountain solution.

EXAMPLE II Samples of the element of Example I were developed 15 seconds at F in a conventional high pH 1- phenyl-3-pyrazolidone/hydroquinone developer in white light, bathed 15 seconds in 2 percent acetic acid, and bleached 30 seconds in a bleach having the following composition:

3 molar potassium bromide (aqueous) 100 ml 3 molar copper (ll) nitrate (aqueous) 50 ml Water 850 ml The bleached strips were bathed 30 seconds in test solutions of the various compounds listed in Table I rubbed with black litho ink using a swab moistened with a working fountain solution prepared as follows:

Stock Fountain Solution:

3 molar orthophosphoric acid l ml 0.5 molar trisodium phosphate 25 ml Water to make 1000 ml Working Fountain Solution:

Stock fountain solution 20 ml Gum Arabic (1 gllOO ml water) 20 ml Diethylene glycol monobutyl ether 50 ml Water to make 1000 ml Other samples were tested using a swab moistened with 2 percent acetic acid. The test solutions were prepared by diluting ml of a concentrated solution of the chosen compound with 95 ml of water. Results of the ink acceptance test are tabulated in Table I following Example Ill.

EXAMPLE III 3 molar copper (ll) nitrate (aqueous) 5 ml Glacial acetic acid 1 ml 3 molar sodium chloride (aqueous) 5 ml 1 molar potassium acetate (aqueous) ml Potassium thiocyanate 4 ml (0.1 g/ml aqueous solution) Water 65 ml 0.3% aqueous colloidal silica sol 10 ml containing about silica Water 100 ml Offset lithographic copies on bond paper were printed on an office duplicator (A.B.Dick) using 1 percent acetic acid as the fountain solution.

TABLE I Ink Acceptance Fountain Concentrated Solution 2% Solution Acetic of Compound Solvent Amount Acid Ex. ll Benzotriazole Ethanol l g/ 100 ml Yes Yes 3,5-dimethyl l.2,4- triazolc Yes No fi nitroquinoline Yes No 2-mercapt0bcnzimid uzole Yes No S-nitrobcnzotriazolc Yes Yes 2-mcrcaptobcnzoxazole Yes No thioglycolic acid Yes No thiobarbituric acid Yes Yes 1,2-naphthotriazolc Yes No 2-mercaptobenzo thiazole Yes No fi-nitrobenzimidazolc nitrate Yes Yes phcnolphthalein Yes No 2-mcrcaptoethanol Yes No Z-mcrcaptothiazolinc Yes Yes 2-mercapto-4- phenylthiazolc Yes No l-phenyl-S- merca totetrazolc Yes No 3-cthy rhodanine Yes No tolutriazole Yes Yes 4-phenylcatechol Yes No 2-chlorobenzothiazole Yes No thiosalicyclic acid Yes No tetrachlorohydroquinone2-amino-6- Yes No methylbenzothiazole 3-amino-l ,2,4- triazole Ethanol l g/lOO ml Yes Yes potassium hexacyanoferrate (11) Water Yes Yes potassium hexcyanoferrate (lll) Yes Yes guanidine thiocyanate Yes Yes Congo red Yes No sodium thiosulfate Yes No potassium thiocyanate Yes Yes S-aminotetrazole monohydrate Yes Yes methyl-7-hydroxyl 2,3-triazoleindolizine 0.26N NaOH 5.2 g/ ml Yes No 6-nitroindazole 20% ethanol/ Yes No 0.2N NaOHl g/IOO ml S-nitroindazole Yes No guanine 0.2N NaOHI g/200 ml Yes Yes ethylenethiourea 50% ethanol] Yes Yes water i g/lOO ml hypoxanthine 0.007N NaOH lg/IOO ml Yes No 3-chloro-6-nitroindazole Ethanol Yes No hexamethylene tetramine Water Yes No phenylisothiocyanate Ethanol Yes No 2,4,5-triphenyl- Yes No imidazole Z-guanidinobenzimidazole Yes No 2-aminobenzimidazole Yes No m,w-bispiperidine methyl urea Water 1 g/ 100 ml Yes No pentamethylene tetrazole Ethanol Yes No DL-B-phenylalanine l% acetic Yes No acid histamine dihydrochloride Water Yes No L-histidine Yes No 1,10-phenanthroline Ethanol Yes No dihydroxynonanophenone Yes No l,2,3-triphenylguanidine Yes No l-phenyl-2-methyl benzimiclazole l g/IOOO ml Yes No 2-methyll ,B-diethyl benzimidazole iodide Yes No l-phenyl-3-ethyl-2- [3 -ethylbenzothiazolepropylidino] benzlmidazolium iodide Yes No 3 l '-disulfopropyl- 5-methyl-2-benzothiazole-2- quinoline cyanine l g/500 ml Yes No Remazol Brilliant Blue (C.l. Reactive blue 19) Water l g/lOO ml Yes No Stilbene Yellow (C.l. Direct Yellow ll) Yes No Condensation product of sodium bisulfite and a polyacrolein resin of molecular weight 400,000. (Carbon to sulfur atomic ratio 6) Water 1 g/lOO ml Yes No tannic acid Yes Yes EXAMPLE IV A sample of the element of Example I was imagewise exposed, developed for 1 minute in a conventional high pH 1-phenyl-3-pyrazolidinone/hydroquinone developer, bathed 15 seconds in 2 percent acetic acid solution, then treated for 30 seconds in an activator of the following composition:

3 molar copper (ll) nitrate (aqueous) ml 3 molar potassium bromide (aqueous) 10 ml 1 molar orthophosphoric acid 5 ml Potassium thiocyanate (0.1 g/ml aqueous solution) 4 ml Sodium nitrite (50 g/liter aqueous solution) 5 ml Water 71 ml The sample was rubbed with lithographic ink using a moistened swab. The imaged portion of the sample accepted ink.

EXAMPLE V A sample of the element of Example I was partially immersed in a conventional high pH p-methylaminophenol/hydroquinone developer for 30 seconds at 68 F, with white room lights turned on. Excess developer was removed by squeegeeing and the sample was bathed seconds in an activator prepared according to the following procedure. Solutions A and B were prepared.

Solution A 3 molar citric acid (aqueous) ml 3 molar tartaric acid (aqueous) 20 ml benzotriazole solution (lg/100 ml of ethanol) 20 ml Water 40 ml Solution B 3 molar potassium bromide (aqueous) 10 ml 3 molar copper (II) nitrate (aqueous) 5 ml Water 85 ml Solution B was added to Solution A.

The treated sample was then squeegeed lightly against the emulsion side of another sample of the element of Example I and held in contact for 45 seconds. The strips were separated and the undeveloped strip was rubbed with lithographic ink using a cotton swab moistened with 2 percent acetic acid. The part of the receptor layer which had been in contact with the developed portion of the first strip accepted ink.

EXAMPLE VI A gelatino-silver image on a polyethylene terephthalate support prepared by conventional photographic methods from the element of Example I was treated in an aqueous copper (II) bromide solution for 10 seconds, then placed in contact with a sample of the element of Example I, also wet with the bleach solution, for 10 seconds, and then separated. The receptor layer was bathed in an aqueous benzotriazole solution for 10 seconds and rubbed with lithographic ink using a cotton swab moistened with 2 percent acetic acid. The receptor layer was found to have an ink receptive image.

EXAMPLE VII A hardened gelatin receptor layer on a polyethylene terephthalate support was prepared by fixing, washing, and drying an undeveloped sample of the element of Example I. Example VI was repeated using this receptor layer in place of the gelatino-silver chlorobromide receptor of that example. An ink-receptive image was obtained on the receptor layer.

EXAMPLE VIII A photographic high speed x-ray type gelatino-silver iodobromide emulsion having a 3/97 mole percent iodide to bromide ratio and containing 120 g of gelatin per mole of silver halide was coated at a coating weight of l 10 mg/dm of silver halide on the subbed polyethylene terephthalate support of Example I. The dried emulsion was overcoated with a gelatin antiabrasion layer having 10 mg/dm of gelatin. Example V was repeated using this element as the photosensitive layer. An ink-receptive image was obtained on the receptor layer.

EXAMPLE IX A sample of the element of Example I was imagewise exposed, developed, and fixed by conventional photographic techniques. The resulting gelatino-silver image and a sample of the element of Example I were bathed for 10 seconds in a solution of the following compositIOIlI 3 molar copper (II) nitrate (aqueous) 5 ml 3 molar potassium bromide (aqueous) 10 ml 3 molar citric acid (aqueous) 10 ml Water ml The bathed strips were placed in contact for 20 seconds and separated. The receptor was bathed for 15 seconds in a solution of the following composition:

Benzotriazole (l g/ 100 ml of alcohol) 10 ml 3 molar citric acid (aqueous) 10 ml Water ml The receptor was then rubbed with lithographic ink using a cotton swab moistened with 2 percent acetic acid containing a small amount of gum arabic. A black ink image appeared on the receptor layer.

EXAMPLE X A hardened gelatin receptor layer on a polyethylene terephthalate support was prepared as in Example VII. Example IX was repeated using this receptor layer in place of the gelatino-silver chlorobromide receptor of that example. A black ink image was obtained on the receptor.

EXAMPLE XI EXAMPLE XII A sample of the element of Example I was exposed and processed as in Example I using instead of the bleach of Example I a bleach of the following composition:

Glacial acetic acid ml Benzotriazole (l gllOO ml of alcohol) 100 ml 1 molar potassium citrate (aqueous) 100 ml 3 molar potassium bromide (aqueous) 50 ml 3 molar copper (ll) nitrate trihydrate (aqueous) 25 ml 1 molar iron (III) nitrate nonahydrate (aqueous) 25 ml 1,2,3-tri henyl guanidine (l gll0(?ml of alcohol) 50 ml Water to make 1000 ml The plate when used as in Example I gave good offset copies free of background scum.

EXAMPLE XIII A high speed ortho-sensitized gelatino-silver iodobromide emulsion having about 1.2 percent silver iodide and containing about 120 g of gelatin per mole of silver halide was coated on an 0.008 inch waterproof, polyethylene coated, photographic base at a coating weight of 27 mg/dm of silver bromide and overcoated with mg/dm of gelatin hardened with 4 g of formaldehyde per 100 g of gelatin.

A sample of this element was exposed on a phototypesetting machine in which each character was separately exposed using a xenon flash tube source having a flash duration of 2 to 3 microseconds and an energy output of 100 millijoules. The exposed sample was tray developed for 30 seconds in a conventional high pH 1- phenyl-3-pyrazolidone/hydroquinone developer containing 0.25 g of benzotriazole per liter, water washed for 30 seconds, and treated for 30 seconds in an activator of the following composition:

Glacial acetic acid 100 ml Benzotriazole solution (1 g/100 ml of ethanol) 100 ml 1 molar potassium citrate (aqueous) 100 ml 0.6 molar potassium bromide (aqueous) 250 ml 0.3 molar copper (ll) nitrate (aqueous) 250 ml Water to ma e 1000 ml The treated sample was then washed with water for 30 seconds and rubbed with a conventional commercial plate treating asphaltum-gum emulsion. The plate was then placed on an offset office duplicating machine (A.B.Dick) and used to print 30,000 copies using a fountain solution prepared as follows.

Stock Fountain Solution 3 molar phosphoric acid 10 ml 0.5 molar trisodium phosphate (aqueous) 25 ml Water to make 1000 ml Working Fountain Solution Stock fountain solution 20 ml Benzotriazole solution (1 g/100 ml of ethanol) 10 ml Gum arabic (l g/100 ml of water) 20 ml Diethylene glycol monobutyl ether 50 ml Water to make 1000 ml All copies showed good quality offset images.

EXAMPLE XIV A high-speed ortho-sensitized aqueous gelatino-silver iodobromide emulsion was coated at 25 mg equivalent AgBr/dm on polyethylene coated, gelatin subbed, waterproof paper base under low intensity red safelights. A gelatin antiabrasion layer containing formaldehyde hardener was coated over the wet emulsion layer at mg/dm and the two layers dried. A 25.4 X 38.1 cm sample of the paper coating was soaked for 1 minute at 22 C. in 1000 ml of water containing 10 g benzotriazole and 1.5 g of the sodium salt of p-tert-octylphenoxydiethyleneglycol sulfonic acid. After air drying, the sample was exposed through a test pattern in a vacuum frame to a K&M, 100-watt, -volt tungsten filament point source incandescent lamp at 114.3 cm for 9 seconds at tap setting 2 (16 volts) and through a glass Wratten (Registered Trademark) 18A UV filter plus a 0.6 neutral density filter. The exposed sample was processed at 22 C. for 40 seconds in a 4-tray processor, e.g., on Agfa-Gevaert Fotorite (Registered Trademark) model DD1437 stabilization paper processor using a conventional high pH l-phenyl-3- pyrazolidone/hydroquinone developer in the first three trays and Solution A in tray 4. Solution A is as follows:

Solution A 3M KBr 50 ml 3M Cu(N0 t,) 3H O 25 ml 10 3M Citric Acid 50 ml 1M Fe(NO;,) 91-1 0 50 ml l-cyanoguanidine (lg/100ml H 0) 50 ml Triphenyl Guanidine (lg/ 100ml ethanol) 50 ml Water up to 1000 ml pH 1.10

The processed sample was then placed on a duplicating machine, e.g., an A. B. Dick 320 Office Duplicator, and using Fountain Solution B 25 good offset copies were made using a black lithographic ink. Fountain Solution B is:

Stock Fountain Solution Described in Example 11 pH 3.9 20 m1 Gum Arabic (lg/100ml H 0) 20 ml Diethylene glycol mono n butyl ether 50 ml Water to make 1000 ml A similarly exposed and processed sample of the same paper emulsion coating which had not been bathed in the benzotriazole solution would not accept ink or give printed offset copies.

EXAMPLE XV An ortho-sensitized gelatino-silver chlorobromide emulsion having a /30 mole percent bromide/chloride ratio and containing 111 g of gelatin per mole of silver halide was coated at a coating weight of 88 mg/dm of silver halide on a polyethylene terephthalate support described in Example 1. The dried emulsion was overcoated with a gelatin antiabrasion layer at a coating weight of 2.5 mg/dm of gelatin hardened with 4.25 g of dimethylolurea per 100 g of gelatin. The prepared photographic film was exposed through a halftone and line test negative for 6 seconds with a 500- watt RSP-Z reflector photospot lamp having a tungsten filament operated at 15 volts at a distance of 127 cm. The exposed photographic film was developed for 30 seconds in the developer solution of Example XIV, except that the developer contained 2 g/liter of benzotriazole, and then activated for 30 seconds at 20 C. in an aqueous bath of the following composition:

3 molar cupric nitrate solution 5 ml 3 molar citric acid solution 10 ml 3 molar potassium bromide solution 10 ml Water ml The activated film was rinsed in water for 5 seconds,

mounted, e.g., on an offset office duplicating machine, and using 2 percent by weight acetic acid as the fountain solution and a lithographic ink good quality negative oleophilic lithographic images were obtained. When a developer was used without any benzotriazole present no oleophilic lithographic image was formed.

EXAMPLE XVI A high-speed, ortho-sensitized gelatino silver iodobromide emulsion having 1.2 mole percent silver iodide and a gelatin to silver halide ratio of 0.36 was coated at a coating weight of 7.2 milligrams of silver bromide per square decimeter on a polyethylene terephthalate photographic film base. The emulsion was overcoated with an antiabrasion layer comprising 10 milligrams per square decimeter of gelatin hardened with 2.96 g of formaldehyde and l 1.25 g of dimethylolurea per g of gelatin. The element was overcoated by skim coating at 38 C. and 2.74 in per minute with a nickel (II) hexacyanoferrate (11) sol prepared as follows:

(4.2% aqueous solution) Solution A was added to Solution B with vigorous stirring. The so] overcoat was then dried with a current of hot air.

The element was exposed through a step wedge and line image transparency for 10 seconds with the K&M light source described in Example XIV at a distance of 127 cm using an ultra violet filter and a neutral density filter of 0.6 optical density. The exposed element was developed for 20 seconds at 22 C. in a conventional high pH hydroquinone/l-phenyl-B-pyrazolidone developer containing 0.25 g of benzotriazole per liter, rinsed in water for seconds, and then activated for 30 seconds at 22 C. in an aqueous bath of the following composition:

3 molar copper (ll) nitrate 25 ml 3 molar potassium bromide 25 ml 3 molar citric acid 100 ml Benzotriazole 0.25 g water to make 1000 ml pH adjusted to 2.0

The plate was then rubbed with a 1 percent aqueous dispersion of colloidal silica and used on an office duplicator-to print offset copies using a lithographic ink and a fountain solution prepared as follows:

A fountain solution concentrate was prepared having the following composition:

3 molar aqueous orthophosphoric acid solution ml 0.5'molar aqueous trisodium phosphate solution 25 ml Water to make 1000 ml The fountain solution was then prepared from the concentrate according to the following formula:

Fountain solution concentrate ml Gum arabic solution (lg/100ml water) 20 ml Diethylene glycol monobutyl ether 50 ml Water to make 1000 ml Satisfactory lithographic images were obtained.

EXAMPLE XVII A nickel (ll) hexacyanoferrate (II) sol was prepared as follows:

Solution A 0.1 molar potassium citrate (aqueous) 20 ml 0.1 molar nickel (ll) nitrate (aqueous) 10 ml Water 170 ml Solution B 0.1 molar otassium hcxacyanoferrate (ll) 30 ml Partial sodium salt of N-lauryl beta iminodipropionate (l g/lOO ml of alcohol) 4 ml Water 166 ml Solution A was added to Solution B in 15 seconds with rapid stirring.

A high-speed, ortho-sensitized gelatino-silver iodobromide emulsion having about 1.2 percent silver iodide and containing about 120 g of gelatin per mole of silver halide, coated at a coating weight of about mg/dm on a smooth, polyethylene coated, photographic paper base was overcoated with the sol by skim coating at a speed of 2.44 m per minute and hot air dry- Two samples were exposed through a step wedge and line image transparency for 10 seconds with a K&M, -watt, 20-volt tungsten point source incandescent lamp at tap setting 2 (16 volts) at a distance of 127 cm using an ultra-violet filter and a neutral density filter of 0.6 optical density. The exposed samples were developed for 30 seconds at 22 C. in a conventional high pH hydroquinone/l-phenyl-3-pyrazolidone developer containing 0.25 g of benzotriazole per liter. One sample was activated for 8 seconds in the following activator solution:

3 molar copper (ll) nitrate 16.3 ml 3 molar potassium bromide 15.5 ml 3 molar citric acid 100.0 ml Benzoquinone 0.79 g Water to make 1000 ml The second sample was activated for 8 seconds in the following activator solution:

3 molar copper (ll) nitrate 25 ml 3 molar potassium bromide 25 ml 3 molar citric acid 100 ml 0.2 molar mercury (11) chloride 50 ml Water to make 1000 ml Each activated sample was dried by hot air and used on an office duplicator to print good offset copies using a lithographic ink and fountain solution described in Example XVI.

EXAMPLE XVlIl Element A is a high-speed ortho-sensitized aqueous gelatino-silver iodobromide emulsion which was coated at 25 mg equivalent AgBr/dm on polyethylene-coated, gelatin-subbed, waterproof paper base under low intensity red safelights. A gelatin antiabrasion layer containing formaldehyde hardener was coated over the wet emulsion layer at 15 mg/dm and the two layers dried. Element B consists of Element A overcoated by skim coating at 38 C. and 2.74 m per minute using a nickel (II) hexacyanoferrate (ll) sol prepared as follows:

Solution A Water 800 ml Nickel (ll) nitrate hexahydrate 0.75 g Potassium citrate monohydrate 0.61 g Solution 13 Water ml Potassium hexacyanoferrate (11) 1.06 g trihydrate Sodium octyl phenoxy ethoxysulfonate (4.2% aqueous solution) 10 ml Solution A was added to Solution B with vigorous stirring. The sol overcoat was then dried with a current of hot air.

Element A was exposed and processed as described in Example XIV. Processed Element A was rewet with solution A described in Example XIV and squeeged in contact with Element B for 30 seconds at 22 C. The elements were separated and Element B was then placed on an offset office duplicating machine and, using Fountain Solution B in Example XIV and a lithographic ink, 10 copies were prepared.

This example was repeated except that prior to the exposure and processing of Element A in the above procedure, both Elements A and B were soaked in a 0.01 molar solution of potassium ferrocyanide for two minutes. Excess solution was drained from the ele' ments and the elements were air dried. Up to 500 offset images were obtained during the printing operation.

The lithographic images of this invention are more easily and rapidly prepared than those used hitherto. Lithographic plates using these images start to print more rapidly, have longer life, and greater resistance to aging than other plates prepared from gelatino-silver halide emulsion layers.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A process for making lithographic images which comprises exposing imagewise a photographic element comprising a support bearing a layer of a dispersion of light-sensitive silver halide in a macromolecular organic protein colloid binder; developing the exposed layer with a silver halide developing agent to form a silver image; treating the developed silver image with an aqueous solution having a pH about 0.5 to 0.6 containmg a. a water-soluble, inorganic copper salt yielding copper (II) ions in a concentration of 0.01 molar to about 2.0 molar,

b. a water-soluble, inorganic halide yielding a halogen ion forming a silver salt no more soluble in water than silver chloride in a concentration of 0.01 to 0.5 molar,

to reduce copper (II) ions, the reduction being terminated before all superficial visible silver image is oxidized, characterized in that an oleophilogenic compound is present (I) at least when the element is treated with the aqueous solution or (2) after formation of copper (I) ions.

2. A process according to claim 1, characterized in that the oleophilogenic compound contains at least one heterocyclic nitrogen atom.

3. A process according to claim 1, characterized in that the copper salt is copper chloride.

4. A process according to claim 1, characterized in that the copper salt is copper bromide.

5. A process according to the preceding claim 1, characterized in that the solution contains c. citric acid in a concentration 0.01 0.25 mole per liter.

6. A process according to the preceding claim 1, characterized in that the oleophilogenic compound is benzotriazole.

7. A process according to claim 1, characterized in that the oleophilogenic compound is potassium thiocyanate.

8. The process of claim 1 wherein the macromolecular organic protein colloid is hydrophilic hardened gelatin.

9. A lithographic printing plate comprising a support and a coplanar image-bearing layer of (A) a macromolecular protein colloid and (B) an oleophilogenic image of an insoluble complex or salt of copper (1) ion with (a) a macromolecular protein colloid and (b) an oleophilogenic compound, reduced visible silver being present within the image areas of said image-bearing layer.

10. The lithographic plate of claim 9 wherein said macromolecular protein colloid is hydrophilic hardened gelatin.

11. A plate according to claim 9, characterized in that the oleophilogenic compound is benzotriazole. 

2. A process according to claim 1, characterized in that the oleophilogenic compound contains at least one heterocyclic nitrogen atom.
 3. A process according to claim 1, characterized in that the copper salt is copper chloride.
 4. A process according to claim 1, characterized in that the copper salt is copper bromide.
 5. A process according to the preceding claim 1, characterized in that the solution contains c. citric acid in a concentration 0.01 - 0.25 mole per liter.
 6. A process according to the preceding claim 1, characterized in that the oleophilogenic compound is benzotriazole.
 7. A process according to claim 1, characterized in that the oleophilogenic compound is potassium thiocyanate.
 8. The process of claim 1 wherein the macromolecular organic protein colloid is hydrophilic hardened gelatin.
 9. A lithographic printing plate comprising a support and a coplanar image-bearing layer of (A) a macromolecular protein colloid and (B) an oleophilogenic image of an insoluble complex or salt of copper (I) ion with (a) a macromolecular protein colloid and (b) an oleophilogenic compound, reduced visible silver being present within the image areas of said image-bearing layer.
 10. The lithographic plate of claim 9 wherein said macromolecular protein colloid is hydrophilic hardened gelatin.
 11. A plate according to claim 9, characterized in that the oleophilogenic compound is benzotriazole. 